Field of the Invention
The present invention relates to a liquid level sensing apparatus, and especially relates to a liquid level sensing apparatus for long-distance automatically enhancing a signal-to-noise ratio.
Description of the Related Art
FIG. 7 shows the first embodiment of the related art liquid level sensing apparatus. A related art liquid level sensing apparatus 50 is arranged on a tank 40. The tank 40 comprises a material entrance 402 and a discharge hole 404. A measured target 20 is arranged in the tank 40. The related art liquid level sensing apparatus 50 transmits a sensing signal 108 to the measured target 20. The sensing signal 108 touches the measured target 20 to reflect back a reflected signal 110. The related art liquid level sensing apparatus 50 receives the reflected signal 110 to measure a signal-to-noise ratio and to measure a distance between the measured target 20 and the related art liquid level sensing apparatus 50. The measured target 20 is, for example but not limited to, grains, gravels or plastic pellets, and so on. The related art liquid level sensing apparatus 50 shown in FIG. 7 is not arranged horizontally, so that the quality of the reflected signal 110 is bad and the reflected signal 110 is not determined easily thus causing incorrect detection, as shown in the upper waveform diagram of FIG. 8.
FIG. 9 shows the second embodiment of the related art liquid level sensing apparatus. The description for the elements shown in FIG. 9, which are similar to those shown in FIG. 7, is not repeated here for brevity. Comparing to the related art liquid level sensing apparatus 50 shown in FIG. 7, the related art liquid level sensing apparatus 50 shown in FIG. 9 is arranged horizontally, but reflecting surfaces of the measured target 20 are uncertainty geometric surfaces thus also causing incorrect detection easily, as shown in the upper waveform diagram of FIG. 10.
FIG. 11 shows the third embodiment of the related art liquid level sensing apparatus. The description for the elements shown in FIG. 11, which are similar to those shown in FIG. 7, is not repeated here for brevity. The measured target 20 shown in FIG. 11 is the ocean or the river and so on. As shown in FIG. 12, the interference signal 114 is too large, but the correct reflected signal 110 is smaller thus causing incorrect detection, as shown in the upper waveform diagram of FIG. 12.
FIG. 13 shows a radiation field pattern of the related art liquid level sensing apparatus. The correct reflected signal 110 received by the related art liquid level sensing apparatus 50 is weaker, but the noise 116 is stronger. The related art liquid level sensing apparatus 50 has wide beam angles and incorrect radiation angles. The signal-to-noise ratio is only 5 dB.